In general, modern electronic devices utilize storage devices, such as hard disc drives, to store vast amounts of data. As electronic devices have become smaller, data storage devices have been designed to store more data in less area. Typically, such storage devices include data channel circuitry to facilitate the transfer of data between the storage device and a host system, such as a processor, a computer, other electronic circuitry, or any combination thereof. Such data channel circuitry typically utilizes data decoding circuitry and error correction circuitry to reliably reproduce data written to and read from a storage medium, such as a rotatable magnetic disc media.
Within data detection circuits, the use of low-density parity check (LDPC) codes and iterative decoding is becoming commonplace in today's magnetic recording systems. In some instances, the channel detector circuitry uses a soft-output Viterbi algorithm (SOVA) detector to estimate hard decisions associated with channel bits of the readback signal. However, correlated bit errors in the detected output can adversely impact the efficiency of the SOVA detector.
Channel preceding is a technique for improving bit and sector failure rates in the presence of correlated bit errors; however, conventional SOVA detectors are not adapted to work with channel precoding, since the SOVA detector cannot be used to compute reliabilities (soft decisions) related to original unprecoded bits directly from reliabilities of the channel bits determined by the conventional SOVA.